def prost(x):
    k = 0
    for d in range(1,x+1):
        if x % d == 0:
            k+=1
    if k == 2:
        return True
    else:
        return False

first_num = 0
second_num = 0
num = ''
s = input().split()
sp_chis = ['zero','one','two','three','four','five','six','seven','eight','nine']
if len(s)!=3 or  s[0]=='0':
    print('wrong input')
else:
    for i in s:
        if i in sp_chis:
            num+=str(sp_chis.index(i))
    for p in range(int(num)+1,1000):
        if prost(p)==True:
            first_num = p
            break
    for p in range(int(num) -1,0,-1):
        if prost(p)==True:
            first_num = p
            break
        if abs(int(num)-first_num) >= abs(int(num)-second_num):
            print(second_num)
        else:
            print(first_num)
            
